Modern cryptographic systems seek to protect the secrecy of information through the application of a mathematical transformation that permutes the information to be protected with a secret, called a key, to produce a cipher text. The cipher text may be subsequently processed using a related key to reverse the transformation and recover the original information at a later time. Symmetric cryptography uses the same secret key to both encrypt and decrypt the information. According to Kerckhoffs's principle, the security of a well-designed cryptographic system rests entirely in the key. An adversary can know all the design and implementation details of the cryptographic system except the secret key, and will be unable to recover the information significantly faster than trying, on average, half of all possible values of the key.
Under some circumstances, an adversary with physical access to or in close physical proximity to the cryptographic system may be able to determine information about the data and especially the keys that is leaked through side-channels such as power consumption measurements or electromagnetic emanations. In such cases, it would be advantageous to provide a method of obfuscating cipher processing of data.